My project is two miles from the nearest pair of monuments that have published coordinates in NAD 83/97. My VRS gives CORS coordinates but my plan set requires NAD 83/97 coordinates. The difference between NAD 83/97 and CORS is approximately two tenths northing and fourteen hundreths easting in this area. I'm going to certify this plan set.
Instead of traversing to establish control at my site, can I use my GPS using VRS and localize off of those two points, and then apply that correction to two points I set at my job site?
Thanks
What you might do:
Take your gps and occupy the 2 points, in question, then occupy several points on your project. NOW you can look at what is going on, yourself. You have NEW coordinates, based on the VRS, on the pair of mons, from 1997, and you have coords on your project site, that are also on that same system.
Think of a traverse, from the pair of mons you mentioned, to the VRS, then to your site. Now, you have some decisions to make. And, you have a quality control, and an idea of accuracy. For something like this, I'd look at the dist from the Pair mentioned above, to the VRS site, then the dist to the project site, and I'd think it all through, WITH how much time is needed, to get your accuracy UP to an acceptable level, and your error management DOWN where it should be.
Just me ramblin....
Of course, if you Have 2-4 GPS units, you can occupy all of these at the same time, and your accuracy goes up.....It'd be the preferable thing to do.
N
I would check with the RT Network administrator, NGS advisor, DOT, and see if somebody already has a transformation worked up so you can collect on the required datum.
Obviously you would want to test to verify that the transformation is correct.
Is post-processing an option?
Occupy The Two Monuments Using VRS...
...occupy as many project points as possible, reoccupy the monuments, adjust all to monuments.
Two miles is as good as 2 meters to GPS.
Paul in PA
Occupy The Two Monuments Using VRS...
Preferably, re-occupy a number of monuments on a different day than the first occupation, just to stay within the standards laid out by Bill Henning at NGS.
http://www.ngs.noaa.gov/PUBS_LIB/NGSRealTimeUserGuidelines.v2.1.pdf
Be careful with the monuments, be sure they are in the passive network, otherwise you just have "converted" monuments to NAD83 from NAD27 values and those could have "errors" larger than .2'. However if they are part of the HARN network you should be fine to use them, but verify the values for them.
The datasheet should say something like "this is a Cooperative Base Network Control Station" and that "the coordinates were established by GPS observations".
Other monuments not in the HARN network will probably state that "horizontal coordinates were established by classical geodetic methods"
These monuments I wouldn't use for 83/97 numbers.
I would simply add the properly computed projection and datum transformation parameters to the controller, then check in to the published monuments. By check in I mean redundant observations. If you check within the project specifications go to work. This assumes the stations you refer to are published at acceptable order for the work.
If you cannot find acceptable control within VRS range, occupy a few static and process yourself. I would augment it with static data from the VRS station(s) if possible. It's like having free units cooking around the clock...
Blowing the StarNet horn
Collect RTK vectors from the virtual base to your old control points, and to the new control points you want to establish. In StarNet (or the LS adjustment package of your choice) hold the NAD83(97) positions of your old control points fixed (more precisely stated- perhaps not fixed, but with a small standard error) and let the virtual base float.
For best results occupy each point at least twice with some time separation between occupations. At least 20 minutes but 4 hours is better.
This really is a routine chore with Least Squares.
Alternatively, most data collectors have some sort of localization routine built in these days.
Thank you land surveyors! I weighed all of your ideas and applied procedures accordingly… The project is moving right along with respect to control that I can be confident with. Thanks again. I appreciate all of you sharing your ideas that were helpful.
rotate and translate much?
